This disclosure directs itself to a reversing configuration control for string instruments that permits switching between various combinations of a pair of electromagnetic pickup coils, either widely separated or collocated in a common enclosure, in one of series or parallel with the pickup coils being of like polarity, a single one of the pickup coils, and in one of series or parallel with the pickup coils being of opposite polarity, one with respect to the other. More in particular, the disclosure is directed to a reversing configuration control for string instruments that includes a pair of pickup coils disposed on a string instrument in which voltages are induced therein responsive to vibration of at least one string of the string instrument and a pair of potentiometers where at least one potentiometer is coupled to one of a pair of output terminals and one displaceable contact of at least one of the potentiometers is electrically connected to one of a pair of input terminals to which the pickup coils are connected. By that arrangement, selective operative coupling of the pair of pickup coils coupled in various configurations to the output terminals is provided. Still further, the disclosure is directed to a system wherein the selective operative coupling between the pair of pickup coils and the output terminals that is provided by the pair of potentiometers additionally selectively provides the effective coupling of only one of the pair of pickup coils to the output terminals. Further, the system can provide selective operative coupling of the pair of pickup coils in combination with the pickup coils having like polarity, selection of a single one of the pair of pickup coils, or can provide selective operative coupling of the pair of pickup coils in combination with one of the pickup coils having an opposite polarity with respect to the other pickup coil.
Electric string instruments, such as electric guitars, electric bases, electric violins, etc., use a pickup to convert the vibration of instrument's strings into electrical impulses. The most commonly used pickups uses the principle of direct electromagnetic induction. The signal generated by the pickup is of insufficient strength to directly drive an audio transducer, such as a loudspeaker, so it must be amplified prior to being input to the audio transducer.
Because of their natural inductive qualities, all magnetic pickups tend to pick up ambient electromagnetic interference (EMI) from electrical power wiring in the vicinity, such as the wiring in a building. The EMI from a 50 or 60 Hz power system can result in a noticeable “hum” in the amplified audio by from the audio transducer, particularly with poorly shielded single-coil pickups. Double-coil “Humbucker” pickups were invented as a way to overcoming the problem of unwanted ambient hum sounds. Humbucker pickups have two coils that are arranged with opposite magnetic poling and corresponding oppositely wound coils to produce a differential signal with respect to signals not generated as a result of the magnetic fields of the pickup. Since ambient electromagnetic noise effects both coils equally and since they are oppositely wound, the noise signals induced in the two coils are canceled out. The two coils of a Humbucker are often wired in series to give a fuller and stronger sound.
While most single coil pickups in multiple pickup installation are wired in parallel with each other, it is also possible to wire them in series, producing a fuller and stronger sound. The two coils of a Humbucker type pickup can also be connected in parallel. This results in a brighter sound, but at the cost of a lower output as with a single-coil pickup, but with the pickup's hum-cancelling properties of the Humbucker still being retained. Using a multiple pole, multiple throw switch, such as a double pole, double throw switch (DPDT) or double pole three position switch, it is known in the art to switch the coil configuration between series and parallel, and may also provide for a “coil cut” configuration (a single coil output).
By reversing the electrical polarity of one of two pickup coils connected in series or parallel, whether in a Humbucker pickup or a configuration of two single pickup coils, the concept of signal cancellation can be applied to the sound signals generated from the strings of the instrument. Signals from the two coils of the same frequency will be cancelled to some degree as a function of the phase and amplitude differences between them. As the string movement adjacent the bridge is less than adjacent the neck of the instrument, the bridge pickup will necessarily generate higher frequencies, including harmonics, than that generated by a neck pickup. To a lesser degree, the same is true for the coils of a Humbucker pickup. The coil of a Humbucker pickup closest to the bridge of the instrument will generate higher frequencies than the coil which is further from the bridge. Musicians have employed this concept to change the sound of their instrument to create particular effects. The reversing of the polarity of one coil relative to the other substantially removes the lower fundamental frequencies in the output signal from the combined pickup coils, leaving the higher frequencies and harmonics. To that end, coil reversing switches have been added to prior art systems.
Blend potentiometers, usually formed by two potentiometers ganged together to be rotated by a single shaft, allow blending together outputs of two pickup coils in varying degrees, not unlike a balance control provided in stereo equipment. Blend potentiometers, however, do not accomplish switching of the coil configuration or coil reversing. In one known prior art system disclosed in U.S. Pat. No. 4,423,654, a tone control formed with a pair of ganged rheostats is connected to the two coils of a Humbucker type pickup. The operation of this tone control provides a series coil configuration at one end of the rotation of the control and a parallel configuration at the opposing end of the rotation thereof. Of the two rheostats used, the resistance element of one is configured to have substantially zero resistance (zero ohms) between one end terminal and the midpoint of the resistance element's length and thereafter increase linearly, while the other rheostat has a resistance that increases logarithmically along its length. Due to the logarithmic taper of the resistance element, from the one end of the travel of the control that provides a series configuration of the coils to and including the midpoint thereof, the series configuration is maintained, changing only the high frequency attenuation included in the control.